Electric furnace.



' W. DI COOLIDGB.

ELECTRIC FURNACE.

APPLICATION FILED SEPT. 2a, 1909. xsmwsn D30. 15. 1911 1,096,414. Patented May 12, 1914.

Inventor: William D. Coolidge,

7 Witnesses FIAT} UMTED IDIBFJGTPUIG COMPANY, J34- {EOE-Ft ELECTRIC? BTU? Application filed September M, 1908, Serial No. 454,

Specification of .cetters He-tent.

Patented May 12, 1914. Renewed December 15, 1911. Serial No. 666,037.

To all whom it may concern Be it known that I, \Vnmnmr D. COOL'iDGE, a citizen of the United States, residing at Schenectady, county of Schenectady, State of New,Yo-rk, have invented certain new and useful Improvements in Electric Fun naces, of which the following is a speciiication.

My present invention relates to electric furnaces and comprises a. furnace of th resistance type suitable for general. use in the arts and having special advantages for the production of very high temperatures, such as are used in the production of lamp filaments of refractory metals and materials.

My improved furnace includes a tube of alumina wound with a heating coil of platinum or other refractory metal. it has a hot zone free from chemically active vapors and well suited for the treatment of mate rials sensitive to contamini-ition by such substances as carbon vapors, or the vapors of silicious material.

'For a. better understanding of my invention, reference may be had to the following detailed description taken in conjunction with the accompanying drawings, in which- Figure 1 is a sectional elevation of a furnace arranged for the treatment of lamp filaments, and Fig. 2 is a perspective view, partly diagrammatic, of a furnace suitable for dental work or general industrial use.

The apparatus illustrated in Fig. 1 comprises a refractory tube '1 of alumina about which is a spiral Winding 2 of platinum ribbon. This alumina tube may be made by electrical methods including actual fusion of the alumina, or may be made by mixing powdered alumina with a binder, such as tar or parafiin, and then baking and firing to a high temperature, say 1400 to 1500 degrees C. in an Arscm vacuum fur-- nace. The platinum ribbon 2 is provided at its ends with terminals or binding posts 3, at whereby electrical energy can be supplied to the platinum strip to heat the alumina. tube. A packing of powdered alumina 5 incloses the platinum winding, except at its extreme ends, and serves not only to prevent radiation of heat outward from the tube, but also prevents contamination of the platinum by gases or vapors such as might be developed by a less refractory packing. In this respect it is far superior to silicicus material. An earthen tube 6 ser es to retain the powdered alumina packing, and this tube is in turn surrounded by asbestos fiber 7 held in an earthenware wt 8. When this furnace is in operation or the production of lamp filaments, the alumina tube stands vertical and is supplied at the top with a stream of hydrogen introduced through a copper tube '9 entering through an asbestos block 10 packed about with asbestos fiber 11 to make a tight joint- .1233 the top of the tube. A water cooled iron tube 12 may be so ported innnediately below the alumina tube and serves a sort of antecliamber whereby filaments or other objects to be treated may be introduced or withdrawn from the hotzone of the alumina tube Without danger of exposure to the air while in a heated and caddie-able condition. The lower end of the iron. tube i may have a stopper 13 of porous fiber, whereby the hydrogen passing through be alinniua tube can escape slowly into the air, or if desired, means may be provided for piping this hydrogen back through a circulating pump and then into the furnace again through the tube 9' "thetop. This latter arrangement effects sa's'in in hydrogen and, furthermore, 1 "his the use of a rapid stream through the hot Zone of the furnace Without undue expense, for by returning the hydrogen to the furnace it may be used again and again with only such small additions. as necessary to compensate for leakage and for such amounts may have been chemicallyuscd up in the treatment of materials in the furnace.

.riccording to a process of lamp filament manufacture, as devised by me and described in other applications, I mix finely divided tungsten or other refractory metal or mate rial with a warm, plastic zlloy of cadmium, mercury and bismuth. This mixture is then extruded through a die to form wires which on subsequent treatment with heat give up their low melting metals in the form of vapor and finally sinter and shrink together into coherent filaments suitable for use in incandescent. lamps. The furnace just t lescribed is of great a'lue as a means f l eftesting the complete removal ojf such metal By ti quiri tick at 75 be- 011 Q13 vapors dangerous -1 that the filaments r011 110 good 11g a the 11C; of c011 free from kinks, 1 Hint they be. no

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means -for raising said filaments into said tube for treatment.

3. A furnace for the treatment of refractory materials, comprising a tube of alumina, a conductor, disposed about said tube for heating it, means for supplying gas to one end of said tube, and a packing of alumina inelosing the hot zone of the tube.

it. In a furnace, the combination of a vertical alumina tube, means for heating said tube, and means for 'aising a plurality of unfinished lamp filaments into the hot Zone of said tube and for withdrawing them therefrom while inclosed in hydrogen.

5. An electric furnace having a tube of s1.1pporting unfinished filaments \vithin said tube, means for supplying gas at one end of the tube, and a cool anteehamber into which the filaments may be moved after heat treatment in said tube.

9. An electric furnace comprising a fused alumina tube, a platinum Winding on the outside of said tube, an alumina packin for said winding, and a heat insulating padliing mclosing said alumina packing.

10.-In a furnace, the combination of a vertical tube closed atits upper end, an electric heating coil surrounding said tube, and an inert packing inclosing said tube and heating coil. F

11. In an electric fu nace, the combination of a tube of alumina having-a heating coil of platinum surrounded by suitable refraetory material.

12. An electric furnace comprising a tube offused alumina, a. heating coil about said tube, and an envelop of refractory material inclosing said coil.

In witness whereof, I have hereunto set my hand this 21st day of September, 1908.

'WILLIAM l). COOLIDGE.

lVitnesses BENJAMIN B. HULL,

MARGARET F. Nooniazr. 

